The present invention relates to a two-battery system and a method for starting and managing the charge of a two-battery system.
German Published Patent Application No. 40 28 242 describes a two-battery system that includes a generator, a starter, a starter battery, a vehicle electrical-system.battery, electrical consumers, and a starter-battery switch, which is connected to a control unit. In this context, electrical consumers are subdivided into primary and secondary consumers. Primary consumers are to be understood as consumers essential to the starting ability and driving ability or vehicle safety, such as the engine control unit and the lights. The secondary consumers are consumers that are primarily responsible for comfort; such as the on-board computer, seat heater, or hi-fi system. The starter-battery switch is arranged between the starter battery and the rest of the vehicle electrical system, while the starter is directly coupled to the.starter battery. The starter-battery switch is switched by the control unit as a function of the charge of the starter battery and the electrical-system battery, and the current supplied by the generator. The starter-battery switch is closed by the control unit during the trip, i.e., when the engine is running, when the generator is supplying current, in order to charge both batteries and simultaneously power the consumers, or when charge equalization occurs to the advantage of the starter battery. The starter-battery switch is always opened when the engine is standing. This prevents the starter battery from being discharged by the closed-circuit current of the consumers or by a discharged electrical-system battery, while standing or driving. A disadvantage of the conventional two-battery system is that the connection between the starter and the starter battery is permanently in-circuit, thereby requiring appropriate, costly protective measures. If, however, the starter lead is switched off-circuit, then the conventional methods for starting and managing the charge of a two-battery system may not be applied.
Therefore, it is an object of the present invention to provide a method for starting and managing the charge of a two-battery system having a fused starter lead, and a two-battery system for implementing the method.
The above and other beneficial objects of the present invention are achieved by providing a method and a system as described herein.
With the exception of the actual starting phase, the control line may be switched off circuit by positioning the electronic pole terminals between the starter battery and the starter, and between the electrical-system battery and the starter. In this case, the start-relevant consumers are permanently assigned to the starter battery, and the electrical-system consumers are permanently assigned to the electrical-system battery. A circuit-breaker, which may be switched by a signal determining the excitation of the generator, is arranged between the electrical-system battery and the starter battery. This allows for extremely simple starting management and charge management of a two-battery system, by which both very large engines may be reliably started and very long immobilization times are possible. In the stopped state, the starter battery may be electrically decoupled from the electrical-system battery by the open circuit-breaker and the blocked electronic pole terminals, so that the starter battery is not loaded by the electrical-system consumers, but only has to satisfy the start-relevant consumers"" very small need for closed-circuit current. Since the closed-circuit currents of the start-relevant consumers are in the mA range, immobilization times of several months are possible. The start-relevant consumers do load the starter battery during vehicle operation, but the currents in the range of 10-16 A are easily compensated for by the energized generator. The electronic pole terminal is blocked again after the starting procedure, and the circuit-breaker is closed after the generator is energized. When fully energized, the generator supplies an output voltage of approximately 14.4 V. Thus, there is always a potential difference between the generator supply point and the two batteries, regardless of whether they are completely charged or discharged. This may ensure that, even when the two batteries are connected in parallel, shunt currents, which may otherwise destroy the circuit-breaker, may not flow from one battery to the other. Therefore, the circuit-breaker enables simple charge management to be realized for the starter battery, it being ensured that the current may only flow from the generator to the two batteries.
Various circuit configurations are possible, depending on the field of application. In order to start large engines that require a large starter current, the two batteries are generally connected in parallel for starting. In this context, the load on the starter battery during the starting procedure is deemed acceptable, since the starter battery is normally recharged to a sufficient extent when the generator is energized. However, in the case of smaller engines, it may be important to load the starter battery as little as possible. To this end, it is standard to only use the electrical-system battery for starting. But, if the electrical-system battery is discharged and the starter battery is charged, then the starter battery is used for starting. If, however, the starter battery is discharged, then an external start may be performed, even when the electrical-system battery is charged, since the start-relevant consumers are no longer powered.
Therefore, a further, example embodiment provides for the circuit breaker receiving a signal from an electrical-system control unit. If the electrical-system battery is charged and the starter battery discharged, then the electrical-system control unit switches the circuit breaker through, so that the electrical-system battery then takes over supplying voltage to the start-relevant consumers in the starting phase. The electrical-system battery may then be used for starting, the electronic pole terminal of the starter battery, e.g., remaining blocked, since a portion of the starter current may otherwise flow through the circuit breaker and possibly ruin it.
But if both batteries are discharged, then an external start may be performed, using an external battery. In this case, only the electronic pole terminal of the starter battery is switched through.